Health Implications of Mercury (Hg) in East Texas Lakes

Larry K. Lowry, PhD The University of Texas Health Center at Tyler Background

There is increasing concern about Hg contamination in East Texas lakes. Hg has potential health impacts on susceptible populations (children, pregnant women, subsistence fisherman, fishing communities, and public health agencies). Some lakes have been posted or have had health advisories issued by State agencies. The press releases Fish advisories for Hg in Texas waters

NW TX

Gulf area Caddo Lake The newspapers, Caddo Lake What to believe? Outline of presentation

The Hg cycle - how Hg enters our food chain Sources of Hg in local lakes Methods for exposure assessment Mercury concentrations in lakes, fish „ Reference values Other topics

Factors affecting Hg accumulation in fish TDH risk assessments-fish advisories Assessment of exposure in humans Risks to susceptible populations The Hg cycle Description, Hg cycle

Mercury enters the atmosphere as Hg vapor „ Incineration, power plants, natural sources „ Evaporation from soil, lakes Mercury is photo-oxidized to inorganic Hg Inorganic Hg deposited in lakes and soil from rain „ Other agents such as oxides of Nitrogen and Sulfur lead to acid rain The cycling of Hg in lakes

Inorganic Hg cycles in lake and sediment Microflora convert inorganic Hg to methyl Hg (organic Hg) Methyl Hg accumulates up the food chain concentrating in the biggest game fish Fisherman catches fish, eats fish Sources of mercury in local lakes

Widespread mercury contamination in most East Texas lakes Not tied to any point source or direct discharge Most likely: „ Coal burning power plants „ Incineration Seems to be associated with acidic lakes „ Is this related to acid rain? Exposure assessment methods

The dose makes the poison - Paraselsus Assess exposure by „ Measurement of Hg in water „ Where in lake? „ How deep? „ Measurement of Hg in fish „ Whole fish: dilutes value „ Edible filet: represents human consumption Total mercury data in East Texas lakes Human health reference value: 0.0122 µg/L (Twidwell, TCEQ, 2000) Reference values, Hg in water

TCEQ „ 0.0122 µg/L WHO „ 0.001 mg/L (1 µg/L) EPA MCL for drinking water „ 0.002 mg/L (2 µg/L) Mercury data in fish from lakes

Prior to 1993, total fish Hg – no problem found 1993 – elevated fish Hg in edible portions in LA, AR lakes Testing in TX using edible portions reveal widespread Hg in fish above advisory levels Reference values for fish

TCEQ „ 0.65 mg/kg (ppm) total Hg in large predator fish (game fish) (0.7 sometimes listed) FDA action level „ 1 ppm (mg/kg) methylmercury „ Limit fish consumption to 7 oz per week „ 0.5 ppm „ Limit fish consumption to 14 oz per week Fish data (Twidwell, TCEQ, 2000)

Only eatable fish tissue analyzed Hg detected in 13 East Texas lake, mostly in large mouth bass. Levels exceeded reference levels in Pruitt lake and Kimball reservoir. Hg levels higher in larger predator fish Fish data by size (Reference value: 0.65 mg/kg, Twidwell, TCEQ 2000) Caddo Lake fish data (Ref value: 0.65 mg/kg,TDH Risk Assessment, 1995)

Fish species Size, in Total Hg, mg/kg (range) Largemouth bass 14-18 (illegal) 0.67 (0.526-0.883)

Largemouth bass > 18 (legal) 1.11 (0.61 –1.63)

Freshwater drum 17-27 1.27 (0.92 –1.53)

Chain pickerel 19-21 0.96 (0.75-1.16)

Channel catfish 14-21 0.21 (0.10 – 0.36) Effect of pH on Hg accumulation in fish (Twidwell, TCEQ, 2000)

When expected Hg concentration in fish is modeled, major factor is lake with acid pH „ Based on expected Hg concentration in fish, pH explains 51% of fish Hg levels „ Correlation of pH with fish Hg shown at right Other contributing factors (Twidwell, TCEQ, 2000)

Total organic carbon (organic matter) Other water chemistry factors Combination of pH and TOC explains 61% of fish Hg levels No correlation of Hg in lake with Hg in fish (Twidwell, TCEQ, 2000)

Examples „ Pruitt and Kimball lakes „ Moderate Hg in water „ Highest pH, TOC, highest levels of Hg in fish „ Other lakes „ Moderate Hg in water „ Normal pH, lower TOC, lower levels of Hg in fish Fish advisories and bans

Mercury shown by (x) TDH fish advisories

Based on risk assessments prepared by TDH What is the basis or reference value?

Older risk assessments (like Caddo Lake) „ Based on EPA reference dose of 0.0003 mg/kg/day with a 10 x margin of safety „ Screening value is 0.65 mg/kg (ppm) for women of childbearing age consuming 30 grams per day. Newer risk assessments „ Based on human exposure data and observed health effect. Same number Exposure assessment in humans

Baseline data from NHANES study Body burden measurements „ Blood „ Urine „ Hair Reference values, Hg in blood Reference values, Hg in urine Reference values, Hg in hair

No established values from NHANES Values from literature „ Drasch, 1997 (Germany) median 0.25 µg/g „ From 150 cadavers with no known exposure to Hg. „ Grandjean, 1992 (Faroe Islands) median 0.8 µg/g „ From 18 islanders with no fish consumption „ Japanese studies – less than 2 µg/g „ Known to be higher in metals than other populations Health effects from consumption of Hg in the diet

Neurotoxic effects most common in adults. „ Tremor, paresthesia (numbness) , ataxia (unstable), malaise, visual disturbances Prenatal exposures, infants „ Developmental delays „ Neurobehavioral changes Effects from fish consumption Three studies with inconclusive results Faroe Islands „ High Hg in fish and whale food „ Some developmental delays, failed to account for other chemical exposures Seychelles „ No effects seen at hair Hg levels seen above New Zealand „ Some effects on psychological and developmental tests, no effects if eliminate one outlier Health effects in susceptible populations

Pregnant women „ Concerns are for developmental disorders in the fetus Children, infant to teen „ Children are more susceptible to developmental disorders and behavioral changes as their systems are developing Subsistence fishermen

Fish advisories are for casual fish eaters „ Example: Caddo Lake, 2 fish meals a month at 2 week intervals for adults (8 oz), children (4oz) What about a subsistence fisherman that eats an 8 ounce serving every day? „ Possibility of substantial dose of Hg and more chronic conditions associated with Hg poisoning „ Fish studies above not conclusive What about others?

What about the pregnant spouse of the subsistence fisherman? What about the risks to children of these families? What about risks to native Americans? Conclusions

Hg in fish pose little risk to most casual eaters of fish, even in those lakes with fish advisories Hg in fish may pose a significant risk to children and to subsistence fisherman and their families through a cooperative agreement

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